Tubes and other containers made of laminated webs, that are in turn fabricated from a metal foil and layers of synthetic resinous materials, are widely used for the packaging of a variety of products, such as toothpaste and the like; American Can Company, of Greenwich, Connecticut, markets such tubular containers under its GLAMINATE trademark. By properly designing and constructing the laminate, the oxygen and moisture barrier properties necessary for the containment of many commodities are afforded, as are the heat sealability and dead fold characteristics that are desirable in a tube-like package. Typically, the product side of the laminate web will comprise an olefinic polymer, such as low density polyethylene, ethylene-acrylic acid copolymer (EAA) or Surlyn ionomer, bonded to the inner surface of the metal layer, which is normally aluminum foil.
Although containers so constructed are entirely satisfactory under most circumstances, the ingredients of certain products have a tendency to degrade or otherwise attack the materials of construction, causing failure of the container. Certain dentifrice products are notoriously difficult to package in such a laminate web structure, particularly those that contain stannous or sodium fluoride as an anticaries agent. Due to the acid environment and/or the essential flavoring oils and detergents that are present, there is a strong tendency for ingredients of the toothpast to permeate the inner plastic layer, and to migrate to the interface, thereby promoting delamination in the web structure and causing deterioration of the contained product. Of course, the longer the period of storage the more pronounced will be the tendency for degeneration to occur in the laminate web, and particularly so if the packaged is stored at a relatively elevated temperature.
Various measures have been in the past not only to enhance the initial level of adhesion achieved between the plastic film and the foil, but also to improve resistance to delamination over extended storage periods, i.e., to extend shelf life. These efforts include flame treatment of the foil, the utilization of interlayers of various adhesive materials, and chemical priming of the metal to increase the strength of the bond at the interface. A notable example of the latter approach entails the utilization of a polyacrylic acid chromium complex product as a foil primer to promote adhesion to polyethylene; laminate structures so produced have been used for the packaging of alcohol-saturated swabs. While the utilization of such a primer is seen to significantly enhance bond strength, still it is not entirely satisfactory on long-term storage, and the use of polyethylene as the product-side layer may be undesirable in some instances, due to the tendency of that material to show environmental stress cracking in the presence of certain products, such as toothpaste.
Accordingly, it is a primary object of the present invention to provide a novel laminate web comprised of aluminum foil and a layer of a copolymer of ethylene with an acrylic acid or acrylic acid ester monomer, which web is adapted for use to contain degenerative products for extended periods of time.
It is also an object of the invention to provide a novel container and package fabricated from such a laminate web.
Additional objects of the invention are to provide novel methods for the production of such webs, containers and packages.